Social evolution is a subdiscipline of evolutionary psychology that is concerned with social behaviours, i.e. those that have fitness consequences for individuals other than the actor. Social behaviours can be categorized according to the fitness consequences they entail for the actor and recipient.

A behaviour that increases the direct fitness of the actor is mutually beneficial if the recipient also benefits, and selfish if the recipient suffers a loss. A behaviour that reduces the fitness of the actor is altruistic if the recipient benefits, and spiteful if the recipient suffers a loss.